The invention relates to transmission of packet-switched data to a wireless terminal, particularly when using addresses according to the IPv6 (version 6 of the IP protocol).
GPRS services (General Packet Radio Service) and packet-switched services of the UMTS system (Universal Mobile Telecommunications System) utilize PDP (Packet Data Protocol) contexts in transmitting user data. PDP contexts are generally logical connections with which the IP data is transmitted from a mobile station to the gateway GPRS support node (GGSN) of the UMTS network, and vice versa. The mobile station is allocated (at least one) PDP address, for which several PDP contexts can be opened in the system. The first context is called a primary PDP context, the following PDP contexts being secondary PDP contexts.
The mobile station knows which application data flows are to be directed into which PDP context tunnel in the transmission of uplink data. In the direction of the downlink, the gateway GPRS support node GGSN must also know packet-specifically which PDP context is used for which data flow received from an external IP network. For this purpose, the destination IP address of the packet is used, and also TFT (Traffic Flow Template) templates are defined for the UMTS. The idea of TFT templates is that the mobile station transmits given values of TCP/UDP/IP address fields to the gateway GPRS support node GGSN for the identification of the flow. The TFT contains one or more so called packet filters. These packet filters allow particularly the arrangement of QoS mapping, i.e. the mapping of packets to the data flow in the UMTS system providing quality of service according to the QoS information of the received packets, e.g. the DiffServ (Differentiated Services) field.
In the UMTS system, it is possible to define the PDP address to be used for the mobile station dynamically or to use a fixed address. Due to the restricted number of IPv4 addresses, the IPv6 is important in the design of the UMTS system. In the UMTS system, the allocation of IPv6 addresses can be implemented using an IPv6 stateless address autoconfiguration mechanism or an IPv6 stateful address autoconfiguration mechanism. The IPv6 addresses are formed of a prefix containing 64 bits and a suffix containing 64 bits. The suffix comprises an interface identifier. It has been suggested for the UMTS system that in order to support the autoconfiguration mechanism of a stateless IPv6 address, a globally unique prefix be allocated to the primary PDP context, in which case the GGSN would use this prefix when transmitting packets from external networks to mobile stations of the UMTS network. This means that all packets having a prefix allocated to a certain mobile station as the destination IP address are transmitted to the mobile station. The GGSN also provides mobile stations with a suffix, which, however, the mobile stations do not have to use. Thus, the mobile stations can determine the suffix used on their own. This, however, involves a security risk, because attackers can transmit packets by using random interface identifiers. Since 64 bits are reserved for a suffix (there being 264 addresses), detecting the attack automatically is virtually impossible. These packets load radio resources, and typically the receiver must also pay for all data he receives. Publication WO 00/41401 discloses a solution according to which the GGSN of the GPRS system can select the PDP context used on the basis of the IP address of the mobile station. The same principle has been in use also in previous 3GPP specifications, according to which the GGSN would determine the right PDP context by using the whole IP address allocated to the mobile station, in which case said problem cannot even have occurred. Thus, however, the solution disclosed in WO 00/41401 does not solve the problem, because the GGSN according to a new suggestion uses only an IPv6 prefix to direct packets to the mobile station, and the mobile station can thus change the interface identifier of its IP address any time. The gateway GPRS support node GGSN involves not only the checking of the prefix but also possible TFT templates, but only one of the secondary PDP contexts can be selected with them to be used as the transmission link for a packet when the filter conditions are met. Thus, the problem is not eliminated by means of TFT template filters, but all packets comprising a prefix allocated to the mobile station are further transmitted to the mobile station.